Tokkai-Hei 04-051466 published by the Japanese Patent Office in 1992 discloses a fuel cell system cooperating with a rechargeable battery. The fuel cell system and the rechargeable battery are connected to a load circuit, supplying the load circuit with electrical power. In this conventional fuel cell system, when the required power for the load circuit exceeds the power generation amount of the fuel cell, the rechargeable battery performs discharge operations. When the required power for the load circuit is less than the generation amount of the fuel cell, excess power produced by the fuel cell is regenerated to the battery.
A fuel-reforming fuel cell system disclosed in Tokkai-Hei 09-007618 published by the Japanese Patent Office in 1997 reduces the capacity of the rechargeable battery cooperating with the fuel cell system by regulating the response speed of the reformer in the fuel cell system according to the rate of change in the required power for the load circuit.